'Milk brain." It's a casual, common slur. Even women use it to describe how disorganized they feel in the first frantic days after giving birth. Yet milk brain is just a temporary effect, brought on by sleep deprivation, plus the need to learn (or relearn) the details of child care.

The lasting effect of being a mother, neuroscientists are finding, is the exact opposite of milk brain."It's interesting to consider what contributed to the myth of the less-than-intelligent maternal brain," says Kelly Lambert, a professor of behavioural neuroscience and psychology at Randolph-Macon College in Virginia.

"A few studies have shown that, even though the moms thought they were impaired or not up to speed, tests failed to show any impairment. So maybe the mom's awareness of any mistakes or shortcomings is enhanced during this maternal period. . . . She is probably doing better than the non-maternal person in a similar situation."

It's true. Blood tests, laboratory experiments with animals and humans, and magnetic-resonance images of working brains reveal that from pregnancy on, female mammals are brighter, bolder and better able to cope with life than their childless counterparts.

These brain improvements are permanent, lasting from the childbearing years into senescence. Nature automatically turbo-charges the brains of mothers. As all kids know, there's a shorthand name for superhuman: mom.

Mothers don't necessarily outshine non-mothers in every possible way, says Craig Kinsley, a professor of neuroscience at Virginia's University of Richmond, and one of Dr. Lambert's senior collaborators. All the same, the behaviours that do improve are so central that they give a new mom an immense advantage over her childless sister. From curiosity to self-confidence to sensory acuteness, the maternal brain shines in a host of ways.

The triggers for maternal brain enhancement involve the same signalling apparatus that governs the whole cascade of life. Puberty, mating, conception, pregnancy and birth are all controlled by chemical messengers called hormones.

Hormones perform a bewildering variety of functions in all mammals, but particularly in females. Estrogens, including a powerful variety called estradiol, are produced in a pregnant woman's ovaries and placenta.

When they travel to the brain, they change it -- a process that until recently was thought to be impossible. Under hormonal direction, brain cells are enlarged in the hypothalamus, a region that strongly affects maternal behaviour.

Hormones increase neuronal branches in a nearby brain area called the hippocampus. The hippocampus isn't directly involved in how mothers behave, but it does play a key role in their general learning and memory. From conception onward, both of these key functions are intensified in moms.

Pregnancy hormones also beef up the brain's amygdala and prefrontal cortices. The amygdala, part of an ancient core brain called the limbic system, regulates intense emotions, including maternal love. The prefrontal areas process sensory input, empathy and conscience.

The upshot of pregnancy, Dr. Kinsley says, is a maternal brain changed forever in critical ways -- not just different, but vastly improved.

In his group's animal experiments, mother rats proved two times better than virgin rats at finding food in mazes, and up to three times bolder in exploring unknown situations.

And in competitions involving multitasking, mother rats beat the tails off their virgin cousins. In every aspect of evolutionary success -- cognition, exploration, adventurousness, general intelligence -- the moms were tops.

Some critics say rats are rats and humans are humans, and never the twain shall meet. Not so, Dr. Kinsley says. All mammals seem to share a common machinery for hormonal brain enhancement. "Mapping the brain circuitry of rats onto that of humans provides strong support for animal models," he says.

For all mammals, it seems, the same maternal machinery has stayed around for millions of years. It works. So why mess with a good thing?

At the Medical University of South Carolina, Jeffrey Lorberbaum, an assistant psychiatry professor, is using magnetic resonance imaging to examine the brains of human mothers listening to the cries of newborns. The mothers, it turns out, can detect their own babies with virtually unfailing accuracy. And they use the same traditional maternal circuits that have been confirmed in rats.

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